Headlamp control circuit

Abstract

A headlamp control circuit reduces a possibility that all headlamps become lights-out in a two-lamp system headlight, even if a switching element fails under a high-beam condition while the single switching element is driven to light two right and left high-beam filaments. A headlamp control circuit includes switch sections (SW 1 ) and (SW 2 ) for lighting low-beam filaments ( 21 ) and ( 31 ), a switch section (SW 3 ) for lighting high-beam filaments ( 22 ) and ( 32 ) together, a diode (D 1 ) for detecting an output voltage on the switch section SW 3 , and a control section ( 120 ) for turning the switch section (SW 3 ) to an on-condition in the case where a high-beam indication is accepted and for turning the switch sections (SW 1 ) and (SW 2 ) to an on-condition in the case where a low-beam indication is accepted and in the case where a high-beam indication is accepted and the diode (D 1 ) detects no high-beam lighting voltage.

1. A headlamp control circuit comprising:
 first and second connecting terminals ( 101 ,  102 ) for outputting low-beam lighting voltages that light first and second luminescent parts ( 21 ,  31 ) to be used as low-beam headlamps, respectively; 
 third and fourth connecting terminals ( 103 ,  104 ) for outputting high-beam lighting voltages that light third and fourth luminescent parts ( 22 ,  32 ) to be used as high-beam headlamps, respectively; 
 first and second switch sections (SW 1 , SW 2 ) for turning on and off supplies of said low-beam lighting voltages to said first and second connecting terminals ( 101 ,  102 ); 
 a third switch section (SW 3 ) for turning on and off together supplies of said high-beam lighting voltages to said third and fourth connecting terminals ( 103 ,  104 ); 
 an output voltage detecting section (D 1 ) for detecting an output voltage on said third switch section (SW 3 ); 
 an indication reception section ( 105 ,  106 ) for accepting a low-beam indication that lights said low-beam headlamps ( 21 ,  31 ) and a high-beam indication that lights said high-beam headlamps ( 22 ,  32 ); and 
 a control section ( 120 ) for turning said third switch section (SW 3 ) to an on-condition in the case where said indication reception section ( 105 ,  106 ) accepts said high-beam indication and for turning said first and second switch sections (SW 1 , SW 2 ) to an on-condition in the case where said indication reception section accepts said low-beam indication and in the case where said indication reception section accepts said high-beam indication and said output voltage detecting section (D 1 ) detects no high-beam lighting voltage. 
 
   
   
     2. The headlamp control circuit of  claim 1 , wherein said control section ( 120 ) comprises:
 a low-beam lighting signal output section (D 2 ) for outputting a signal that turns said first and second switch sections (SW 1 , SW 2 ) to an on-condition in the case where said indication reception section accepts either said low-beam lighting indication or said high-beam lighting indication; 
 a high-beam lighting signal output section ( 123 ) for outputting a signal that turns said third switch section (SW 3 ) to an on-condition in the case where said indication reception section ( 105 ,  106 ) accepts said high-beam lighting indication; and 
 a forced-off section for compulsorily turning said first and second switch sections (SW 1 , SW 2 ) to an off-condition in the case where said output voltage detecting section (D 1 ) detects said high-beam lighting voltage. 
 
   
   
     3. The headlamp control circuit of  claim 1 , wherein said third switch section (SW 3 ) is a semiconductor switch. 
   
   
     4. The headlamp control circuit of  claim 1 , wherein said third switch section (SW 3 ) further includes a self protecting section ( 117 ) for chopping an output voltage when an abnormal condition is detected, and
 wherein a low-pass filter is provided in a signal transmitting path extending from said third switch section (SW 3 ) through said output voltage detecting section (D 1 ) and said control section ( 120 ) to said first and second switch sections (SW 1 , SW 2 ), wherein said low-pass filter smoothes the chopped output voltage to turn said first and second switch sections to the on-condition. 
 
   
   
     5. The headlamp control circuit of  claim 1 , wherein said control section comprises:
 a DRL (Day-time Running Light) control circuit for outputting a control signal indicating a DRL mode; and 
 a PWM (Pulse Width Modulation) generating circuit for generating a PWM signal of a predetermined duty ratio in response to the DRL mode control signal, wherein the PWM signal is applied to the first and second switch sections and the first and second switch sections are turned to the on-condition and the off-condition at the predetermined duty ratio. 
 
   
   
     6. The headlamp control circuit of  claim 5 , wherein the predetermined duty ratio is 80%. 
   
   
     7. The headlamp control circuit of  claim 1 , wherein said control section ( 120 ) comprises:
 a DRL (Day-time Running Light) control circuit for outputting a control signal indicating a DRL mode; and 
 a PWM (Pulse Width Modulation) generating circuit for generating a PWM signal of a predetermined duty ratio in response to the DRL mode control signal, wherein the PWM signal is applied to the third switch section and the third switch section is turned to the on-condition and the off-condition at the predetermined duty ratio. 
 
   
   
     8. The headlamp control circuit of  claim 7 , wherein the predetermined duty ratio is 80%. 
   
   
     9. A headlamp control circuit comprising:
 first and second connecting terminals for outputting low-beam lighting voltages that light first and second luminescent parts ( 91 ,  92 ) to be used as low-beam headlamps, respectively; 
 third and fourth connecting terminals for outputting high-beam lighting voltages that light third and fourth luminescent parts ( 93 ,  94 ) to be used as high-beam headlamps, respectively; 
 first and second switch sections (SW 1 , SW 2 ) for turning on and off supplies of said low-beam lighting voltages to said first and second connecting terminals; 
 a third switch section (SW 3 ) for turning on and off together supplies of said high-beam lighting voltages to said third and fourth connecting terminals; 
 an indication reception section for accepting a low-beam indication that lights said low-beam headlamps and a high-beam indication that lights said high-beam headlamps; and 
 a control section for turning said third switch section to an on-condition in the case where said indication reception section accepts said high-beam indication and for turning said first and second switch sections to an on-condition in the case where said indication reception section accepts said low-beam indication and in the case where said indication reception section accepts said high-beam indication. 
 
   
   
     10. The headlamp control circuit of  claim 9 , wherein said control section comprises:
 a DRL (Day-time Running Light) control circuit for outputting a control signal indicating a DRL mode; and 
 a PWM (Pulse Width Modulation) generating circuit for generating a PWM signal of a predetermined duty ratio in response to the DRL mode control signal, wherein the PWM signal is applied to the third switch section and the third switch section is turned to the on-condition and the off-condition at the predetermined duty ratio. 
 
   
   
     11. The headlamp control circuit of  claim 10 , wherein the predetermined duty ratio is 80%.